There are always things you can’t say they are absolute. Most time, for most subject, how to deal with a concrete situation, it depends on the context. Is there any principle for any context? Oh yeah, there is one, that is, “it depends”. Well, there is actually another one, “don’t be rigid”.
http://www.thekua.com/atwork/2008/08/defensive-programming-depends-on-context/
Jack Ma, a software developer 
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